Vibrational properties of epitaxial graphene buffer layer on silicon carbide

TL;DR

This study uses first-principles calculations to analyze the vibrational properties of the graphene buffer layer on silicon carbide, revealing phonon behaviors that explain Raman signals and implications for thermoelectric applications.

Contribution

It provides a detailed first-principles analysis of vibrational properties of epitaxial graphene on SiC, highlighting phonon behavior despite structural disorder.

Findings

Graphene buffer layer exhibits quasidispersive phonons similar to free graphene.

Vibrations related to thermal conduction delocalize on the SiC substrate.

Results suggest potential for thermoelectric applications due to spatial separation of transport properties.

Abstract

The vibrational properties of semiconducting graphene buffer layer epitaxially grown on hexagonal silicon carbide are determined using first-principles calculations on a realistic structural model. Despite the important chemical and structural disorder associated with the partial covalent bonding with the substrate, the buffer-layer carbon atoms still display quasidispersive phonons mimicking those of graphene. The related frequency softening and broadening provide a natural interpretation of the measured Raman signal. The vibrations determining thermal conduction are found to delocalize completely on the SiC substrate, leading to an effective spatial separation between material components determining, respectively, electronic and thermal transport properties. This situation opens perspectives for thermoelectric applications.